1. Field of the Invention
The present invention relates to an improved fecal occult blood test having a matrix such as paper that is treated, imprinted or impregnated with a test reagent capable of undergoing a chromogen reaction. More particularly, the present invention relates to an improved developing solution for fecal occult blood tests.
2. Background of the Technology
Advances in medical science have led to the development of diagnostic tests for detecting various conditions. With many diseases, it is imperative that early diagnosis be made so that treatment may be administered when most effective.
The presence of occult (i.e., unseen) blood in fecal material has been found to be an early sign of gastrointestinal cancer. Frequently, when blood from internal bleeding becomes visible, the cancer has progressed to a late stage. Because early detection of gastrointestinal cancer is vital to successful treatment, it is important to detect the presence of blood before the blood from internal bleeding becomes visible in fecal material.
Specimen test slides and procedures for detecting fecal occult blood are well known. For example, U.S. Pat. No. 3,996,006 discloses slides having a specimen receiving sheet between a front panel and a rear panel, with openings in the panels and pivotal covers or flaps to cover these openings. The specimen receiving sheet is generally an absorbent paper printed or impregnated with a guaiac reagent.
In operation, a sample of fecal matter is smeared onto the guaiac paper through an opening on the front panel. The panel is then covered, and the flap of the rear panel is opened. A developing solution such as hydrogen peroxide is applied to the guaiac paper via the corresponding opening in the rear panel. Because guaiac is not soluble in water, traditional developing solutions for fecal occult blood tests include alcohol; therefore, the developing solutions have been referred to as “alcoholic peroxides.” A typical formulation for such developing solutions is 5% hydrogen peroxide, 70% ethanol and 25% water. The water to alcohol (i.e., ethanol) ratio in such traditional developing solutions is, therefore, 25/70 or about 0.357.
If blood is present in the sample of fecal matter, the guaiac reaction will turn the paper blue. The guaiac, therefore, functions as a chromogen such that in the presence of hemoglobin (i.e., blood), which functions as a catalyst, oxygen is released from the developing solution, and the oxygen causes the guaiac to oxidize and change from essentially colorless to blue.
Tests for detecting blood in fecal samples before it is visible are extremely useful. Such tests, however, suffer from certain problems and deficiencies. One of the problems with the current fecal occult blood tests is the number of false negatives, i.e., negative test results in samples of bleeding patients. The test is not sensitive enough to pick up lower levels of blood in the feces.
Previous attempts have been made to increase the sensitivity of the test. For example, to detect smaller quantities of fecal occult blood, “enhancing” reagents have been included in the developer. These enhancers include parabens and tertiary amine compounds and their related analogues. For example, U.S. Pat. Nos. 5,310,680 and 5,391,498 disclose the use of phenolic-type compounds such as esters of hydroxybenzoic acid, as well as phenol, guaiacol, 3,5-dimethylphenol, methyl salicylate, 3,5-dichlorophenol, paranitrophenol and parabromophenol. It is arguable whether these enhancers actually change the sensitivity or merely make the chromogenic reaction, i.e., the color change of the guaiac, more readily visible.
Hydration of the smear prior to development has also been employed in an attempt to increase the sensitivity. While it has been suggested that hydration provides greater sensitivity, no meaningful data is available as to the amount of hydration. Furthermore, according to U.S. Pat. Nos. 5,310,680 and 5,391,498, hydration adversely affects the specificity of the test, particularly by producing unacceptable false positive rates, i.e., positive reactions without fecal occult blood present, by reacting with other interfering substances such as vegetable peroxidases.
A need still exists, however, for fecal occult blood tests with greater sensitivity.